<DisplayTemplate>
@{
var product = context as Product;
int currentCellValue = (int)product.ProductCategoryId;
var nestedItem = NestedDataSource.Where(x => x.SubcategoryID == currentCellValue).FirstOrDefault();
string category = nestedItem != null ? nestedItem.Category.ToString() : "none";
string subcategory = nestedItem != null ? nestedItem.Subcategory : "none";
<span>
@category/
@subcategory</span>
}
</DisplayTemplate>